Any other provision of law to the contrary notwithstanding, from March 29, 1957 to December 31, 1957, opportunity to enroll or reenroll in the retirement system with credit for prior service together with service from July 1, 1947, to date of entrance shall be afforded each employee who did not enroll in the system, or who enrolled and has withdrawn his membership or who at the time of the establishment of the system was ineligible, but under provisions of chapters 34 to 36, inclusive, of this title is now eligible, by making application to the board and paying contributions in the amount of that made by a member receiving equal compensation who began contributing when the system was established together with compound interest thereon at the rate of five per cent (5%) per annum. Such contributions may be paid in a lump sum or prorated over a period of time not to exceed two (2) years. Any employee desiring to make such deferred contributions may have the same deducted in equal monthly instalments from his or her salary, in addition to deductions for current instalments. Provided that no person given credit after January 1, 1950, for prior service shall be entitled to retirement hereunder until all unpaid contributions due from such member shall have been paid in full and until the amount due therefor from the employer has been appropriated and paid in to the retirement system. Such appropriation shall be determined on the basis of the first actuarial valuation of the retirement system to be performed after December 31, 1957, and shall be an addition to the regular contribution for current service and prior service for the biennium beginning July 1, 1959, as provided by law.